1. Field of the Invention
The invention is generally related to lifting jacks and more specifically to jacks having a safety mechanism to prevent unanticipated movement from an extended position to a retracted position.
2. Description of the Related Art
A great variety of jacks are known in the field. Jacks are employed to lift items of substantial weight to include vehicles. In some instances, once an item is lifted it may be desired to maintain the item in the elevated position for an extended period while activity is conducted about the item. In these instances, there exists a hazard that the particular jack may lose lifting force engagement, permitting the weighty item to unexpectedly lower. This presents a particularly serious hazard to activity being conducted underneath the item. For this reason the field of art practices placing rigid supports or jack stands under items to prevent the item from lowering in case the jack loses lifting force.
The prior art possesses a variety of exemplary adjustable jacks and jack stands. The following are a few examples.
U.S. Pat. No. 4,042,202 issued to D. Molinari on Aug. 16, 1977, discloses a jack stand with a safety-locking device whereby a pin is positioned through a plurality of alignable corresponding holes in the shaft and the housing locking these members with respect to each other longitudinally. The pin is keyed so as to prevent withdrawal of the pin until rotated into an aligned position.
U.S. Pat. No. 4,479,634 issued to R. Blatz on Oct. 30, 1984, discloses a jackable stand comprising of a vertical post that projects upward normal to a base. A carriage is attached to the vertical post moveably along the length of the post. The post has receiver holes vertically spaced apart along a length of the post and extending through the post. The carriage and base are engageable by a jack that may employ mechanical advantage to progress the carriage along the length of the post. A pin is employed in a selected receiver hole to restrict movement of the carriage along the post.
U.S. Pat. No. 6,027,102 issued to Krupa on Feb. 22, 2000, discloses a hydraulic jack stand having a hydraulic bottle jack positionable on an elongated jack support comprising a tubular outer housing, a moveable cylindrical member, and a pin. The outer housing has a pin anchor receiver, such that the pin may be inserted through the outer housing. The moveable member has a plurality of receiver holes vertically spaced apart along a length that, with the moveable member inserted into the outer housing, may be selectively alignable with the anchor receiver such that the pin may be inserted through both a receiver hole and the anchor hole, fixing the outer housing and moveable member longitudinally.
U.S. Pat. No. 6,322,062 B1 issued to Conn et al. on Nov. 27, 2001, discloses a cabinet installation lifting system comprising a jack and a pair of extendable supports, wherein said supports each comprise a tubular outer housing having an pin anchor receiver, a moveable cylindrical member having a plurality of receiver holes vertically spaced apart along a length that, with the moveable member inserted into the outer housing, may be selectively alignable with the anchor receiver such that a pin may be inserted through both a receiver hole and the anchor hole, fixing the outer housing and moveable member longitudinally throughout the lifting range of the jack.
U.S. Pat. No. 6,443,413 B1 issued to Hawkins et al. on Sep. 3, 2002, discloses an adjustable jack stand having a ratchet and pawl height maintenance mechanism with a pin and hole mechanism wherein the holes in the post coordinate with the teeth in the post so that any engagement between the pawl and a tooth ensures that a pair of holes in the base and the post are aligned to receive a pin.
It would be an improvement to the art to provide a jack having a locking mechanism comprised of a prop exterior to the lifting arm, a storage well for receiving the prop in a retracted position, and a locking pin engagable with said prop to bias said prop and the body of the jack to selectively prevent lifting arm retraction.